In order to increase output power of a semiconductor laser device, a plurality of unit semiconductor laser chips are stacked one on another to make a stacked semiconductor laser device.
FIG. 14 is a front view illustrating a prior art stacked semiconductor laser device. In the figure, reference numeral 5 designates a heat sink. A first unit semiconductor laser chip 1 is bonded to the heat sink 5 with solder 7. Likewise, second, third, and fourth unit semiconductor laser chips 2, 3, and 4 are successively stacked one on another on the first unit semiconductor laser chip 1. Each semiconductor laser chip includes an active layer 6, an upper electrode 9, and a lower electrode 10. A wire 8 is bonded to the upper electrode 9 of the fourth unit semiconductor laser chip 4. Hereinafter, for simplification, the stacked semiconductor laser device is referred to as a stacked laser device and a unit semiconductor laser chip is referred to as a laser chip.
A method of fabricating the prior art stacked laser device will be described.
Initially, the solder 7 is applied to the heat sink 5, and the first laser chip 1 is put on the heat sink 5 so that the lower electrode 10 contacts the solder 7, followed by heating to the solder 7 adheres to the heat sink 5 to the lower electrode 10 of the first laser chip 1. Thereafter, the solder 7 is applied to the upper electrode 9 of the first laser chip 1 and the second laser chip 2 is put on the first laser chip 1 so that the lower electrode 10 of the second laser chip 2 contacts the solder 7 on the first laser chip, followed by heating so the solder 7 adheres to the upper electrode 9 of the first laser chip 1 to the lower electrode 10 of the second laser chip 2. The above-described process is repeated with respect to the remaining third and fourth laser chips 3 and 4, thereby completing the structure shown in FIG. 14 in which the first to fourth laser chips 1 to 4 are stacked on one another through the solder 7. Finally, the wire 8 is bonded to the upper electrode 9 of the fourth laser chip 4 to complete the stacked laser device.
The prior art stacked laser device has the following drawbacks.
First, when the laser chips are stacked one on another, the solder 7 unfavorably flows over the side surface of, for example, the first laser chip 1 as shown in FIG. 14, resulting in short-circuiting between the upper electrode 9 and the lower electrode 10 of the first laser chip. Second, when the solder 7 between two adjacent laser chips, for example, the second and third laser chips 2 and 3, is molten to adhere the upper and lower electrodes of these laser chips, the solder 7 between the first and second laser chips 1 and 2 is also molten and these laser chips 1 and 2 are unfavorably moved. As a result, the precision in aligning the laser chips is degraded.